In recent years, the demand for wind energy has increased in relation to the decreasing supplies and increasing prices of fossil fuels. As a result, windmills or “wind turbines” have grown in both size and numbers. In some locations, farms of modern wind turbines have been erected within miles of critical radar systems, such as commercial air traffic control and military defense radar systems. These “wind farms” are having an increasingly detrimental effect on the performance of nearby radar systems.
First of all, each of these modern wind turbines often has a relatively large radar cross-section (RCS) due to its large mast and blades. For example, many modern wind turbines are being constructed with three 25-75 meter blades rotatably mounted on a mast that is 80-120 meters in height. Some of these wind turbines have been calculated to have an RCS between approximately 40 and 50 dBm2. Such an RCS can cause interference that lowers the sensitivity of a radar system. Moreover, taller masts have placed these large turbine blades within reach of faster moving air currents, but have also made them more visible to surrounding radar systems.
Second, the rotational velocity of wind turbine blades has also increased, with blade tips sometimes approaching speeds generally associated with that of aircraft (e.g., approximately 200 m/s). Therefore, each rotating blade of a wind turbine may cause Doppler reflections perceived by a radar system to resemble a moving target of interest. In many instances, quickly rotating wind turbine blades have been responsible for radar systems generating false target reports.
In the fields of civilian and military aircraft radar, various techniques are used to distinguish between genuine aircraft targets and nonessential radar clutter. For example, in radar systems located on the ground, moving target detection (MTD) filters are used to remove reflected radar targets having velocities below a predetermined threshold value. Such filters are generally effective in preventing low-speed and stationary objects from appearing on radar screens. However, certain moving objects, such as modern wind turbines, are especially difficult to distinguish from aircraft radar signatures, using only traditional radar processing and filter techniques. Specifically, because each wind turbine has a nominal effective velocity at its rotor, each blade rotating about the rotor exhibits a large range of detectable velocities between naught (near the rotor) and velocities increasing radially outwardly from the rotor to a maximum velocity at the tip of the blade. The corresponding range of Doppler reflection frequencies caused by the blade may render MTD filters ineffective.
Accordingly, various alternative approaches have been used to mitigate the rotational effects of wind turbines on aircraft radar systems. For example, attempts have been made at reducing mast height or relocating wind turbines away from radar systems, generally to the detriment of turbine power output. Most other techniques involve modifying wind turbine geometry or materials, adjusting the radar line-of-sight, or implementing complex radar processing methods. Unfortunately, these methods are often costly, difficult to implement, and ineffective. Moreover, many existing radar systems are not capable of being readily updated with wind turbine mitigation processing. As a result, some radar systems simply block out, or “mask” areas located over known wind turbine farms. This technique compromises radar accuracy and prevents aircraft from being tracked over wind farms.
Accordingly, there is a need for improved techniques for mitigating the effects of wind turbines on radar systems.
The systems and methods of the present disclosure solve one or more of the problems set forth above.